Over many years there has been a constant need for small, cheap and efficient power supplies. This has led to the development of Switch-Mode Power Supplies (SMPS). The size of modern power supplies are mainly governed by the passive energy storing elements, which scales inversely with the switching frequency. Therefore, much development has been devoted to increasing switching frequencies. Commercially available converters today switch at frequencies up to several megahertz and can have efficiencies of more than 95%. The reason for not increasing the switching frequency further and thereby reaching even higher power densities are switching losses. One way of addressing this issue has been the use of resonant Radio Frequency (RF) amplifiers (inverters) combined with a rectifier for DC-DC converters. With this type of converters, SMPSs with switching frequencies in the Very High Frequency range (VHF, 30-300 MHz) have been designed with efficiencies up to approx. 90%. By operating the DC-DC converters at radio frequencies, or even at VHF frequencies, it is possible to reduce the size, and thereby also price, of the passive energy storing elements significantly. However, the inductive components, and in particular the power transformers, are still the largest components in the circuits. Therefore, there is a need for small and highly efficient transformers.
Object of the present invention is therefore to provide a transformer for radio frequency operation, with a small and efficient design that can be reliably produced at low cost.